The demand for more effective educational systems coupled with advances in computing and communication technologies have fueled the growth of a broad range of adaptive learning technologies. The resulting applications, tools, and ecosystems, which customize learners’ experiences based on pre-existing user data and/or continuous user inputs, claim to support the acquisition of content knowledge and facilitate the mastery of skills through personalized learning experiences, both formal and informal. These adaptive systems are widespread, although sometimes unrecognized even by those using them.